Resist composition and patterning process

ABSTRACT

A resist composition comprising a base polymer and a quencher in the form of an iodonium salt of fluorinated aminobenzoic acid, fluorinated nitrobenzoic acid or fluorinated hydroxybenzoic acid offers a high dissolution contrast and minimal LWR independent of whether it is of positive or negative tone.

CROSS-REFERENCE TO RELATED APPLICATION

This non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2017-028673 filed in Japan on Feb. 20,2017, the entire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

This invention relates to a resist composition comprising a quencher inthe form of an iodonium salt capable of generating fluorinatedaminobenzoic acid, fluorinated nitrobenzoic acid or fluorinatedhydroxybenzoic acid and a pattern forming process.

BACKGROUND ART

To meet the demand for higher integration density and operating speed ofLSIs, the effort to reduce the pattern rule is in rapid progress. Thewide-spreading flash memory market and the demand for increased storagecapacities drive forward the miniaturization technology. As the advancedminiaturization technology, manufacturing of microelectronic devices atthe 65-nm node by the ArF lithography has been implemented in a massscale. Manufacturing of 45-nm node devices by the next generation ArFimmersion lithography is approaching to the verge of high-volumeapplication. The candidates for the next generation 32-nm node includeultra-high NA lens immersion lithography using a liquid having a higherrefractive index than water in combination with a high refractive indexlens and a high refractive index resist film, EUV lithography ofwavelength 13.5 nm, and double patterning version of the ArFlithography, on which active research efforts have been made.

Chemically amplified resist compositions comprising an acid generatorcapable of generating an acid upon exposure to light or EB includechemically amplified positive resist compositions wherein deprotectionreaction takes place under the action of acid and chemically amplifiednegative resist compositions wherein crosslinking reaction takes placeunder the action of acid. Quenchers are often added to these resistcompositions for the purpose of controlling the diffusion of the acid tounexposed areas to improve the contrast. The addition of quenchers isfully effective to this purpose. A number of amine quenchers wereproposed as disclosed in Patent Documents 1 to 3.

As the pattern feature size is reduced, approaching to the diffractionlimit of light, light contrast lowers. In the case of positive resistfilm, a lowering of light contrast leads to reductions of resolution andfocus margin of hole and trench patterns.

For mitigating the influence of reduced resolution of resist pattern dueto a lowering of light contrast, an attempt is made to enhance thedissolution contrast of resist film. One such attempt is a chemicallyamplified resist material utilizing an acid amplifying mechanism that acompound is decomposed with an acid to generate another acid. Ingeneral, the concentration of acid creeps up linearly with an increaseof exposure dose. In the case of the acid amplifying mechanism, theconcentration of acid jumps up non-linearly as the exposure doseincreases. The acid amplifying system is beneficial for furtherenhancing the advantages of chemically amplified resist film includinghigh contrast and high sensitivity, but worsens the drawbacks ofchemically amplified resist film that environmental resistance isdegraded by amine contamination and maximum resolution is reduced by anincrease of acid diffusion distance. The acid amplifying system is verydifficult to control when implemented in practice.

Another approach for enhanced contrast is by reducing the concentrationof amine with an increasing exposure dose. This may be achieved byapplying a compound which loses the quencher function upon lightexposure.

With respect to the acid labile group used in (meth)acrylate polymersfor the ArF lithography, deprotection reaction takes place when aphotoacid generator capable of generating a sulfonic acid havingfluorine substituted at α-position (referred to “α-fluorinated sulfonicacid”) is used, but not when an acid generator capable of generating asulfonic acid not having fluorine substituted at α-position (referred to“α-non-fluorinated sulfonic acid”) or carboxylic acid is used. If asulfonium or iodonium salt capable of generating an α-fluorinatedsulfonic acid is combined with a sulfonium or iodonium salt capable ofgenerating an α-non-fluorinated sulfonic acid, the sulfonium or iodoniumsalt capable of generating an α-non-fluorinated sulfonic acid undergoesion exchange with the α-fluorinated sulfonic acid. Through the ionexchange, the α-fluorinated sulfonic acid thus generated by lightexposure is converted back to the sulfonium or iodonium salt while thesulfonium or iodonium salt of an α-non-fluorinated sulfonic acid orcarboxylic acid functions as a quencher.

Further, the sulfonium or iodonium salt capable of generating anα-non-fluorinated sulfonic acid also functions as a photodegradablequencher since it loses the quencher function by photodegradation.Non-Patent Document 1 points out that the addition of a photodegradablequencher expands the margin of a trench pattern although the structuralformula is not illustrated. However, it has only a little influence onperformance improvement. There is a desire to have a quencher forfurther improving contrast.

Patent Document 4 discloses a quencher of onium salt type which reducesits basicity through a mechanism that it generates an amino-containingcarboxylic acid upon light exposure, which in turn forms a lactam in thepresence of acid. Due to the mechanism that basicity is reduced underthe action of acid, acid diffusion is controlled by high basicity in theunexposed region where the amount of acid generated is minimal, whereasacid diffusion is promoted due to reduced basicity of the quencher inthe overexposed region where the amount of acid generated is large. Thisexpands the difference in acid amount between the exposed and unexposedregions, from which an improvement in contrast is expected. Despite theadvantage of improved contrast, the acid diffusion controlling effect israther reduced.

As the pattern feature size is reduced, edge roughness (LWR) is regardedsignificant. It is pointed out that LWR is affected by the segregationor agglomeration of a base polymer and acid generator and the diffusionof generated acid. There is a tendency that as the resist film becomesthinner, LWR becomes greater. A film thickness reduction to comply withthe progress of size reduction causes a degradation of LWR, whichbecomes a serious problem.

CITATION LIST

-   Patent Document 1: JP-A 2001-194776-   Patent Document 2: JP-A 2002-226470-   Patent Document 3: JP-A 2002-363148-   Patent Document 4: JP-A 2015-090382-   Non-Patent Document 1: SPIE Vol. 7639 p 76390 W (2010)

DISCLOSURE OF INVENTION

For the acid-catalyzed chemically amplified resist material, it isdesired to develop a quencher capable of providing a high dissolutioncontrast and reducing LWR.

An object of the invention is to provide a resist composition whichexhibits a high dissolution contrast and a reduced LWR, independent ofwhether it is of positive tone or negative tone; and a pattern formingprocess using the same.

Triphenylsulfonium has a molecular weight of 263 and diphenyliodoniumhas a molecular weight of 281. The latter has a higher molecular weight.This is accounted for by the higher molecular weight of iodine althoughthe number of phenyl groups in the iodonium salt is less by one. It isthus concluded that the iodonium salt having a higher molecular weightis more effective for suppressing acid diffusion.

In addition, the iodonium salt has a higher solubility in solvents thanthe sulfonium salt. A quencher having a higher solvent solubility isuniformly dispersed in a resist solution and uniformly dispersed in aresist film after coating. The uniform dispersion of the quencher in theresist film ensures uniform acid diffusion, leading to improvements inedge roughness (LWR) of line pattern or dimension uniformity (CDU) ofhole pattern.

The inventors have found that using an iodonium salt of fluorinatedaminobenzoic acid, fluorinated nitrobenzoic acid or fluorinatedhydroxybenzoic acid as the quencher, a resist material having a reducedLWR, high contrast, improved resolution, and wide focus margin isobtainable.

In one aspect, the invention provides a resist composition comprising abase polymer and a quencher containing an iodonium salt having theformula (A).

Herein R¹ is a nitro group, hydroxyl group or a group having the formula(A-1) below, R² is fluorine or trifluoromethyl, R³ is methyl or cyano,R⁴ is hydroxyl, halogen, trifluoromethyl, nitro, carboxyl, a C₂-C₁₀ acylgroup, C₂-C₁₀ acyloxy group, C₂-C₁₀ alkoxycarbonyl group, a straight,branched or cyclic C₁-C₁₂ alkyl group which may contain oxo, a straight,branched or cyclic C₂-C₁₂ alkenyl group which may contain oxo, astraight, branched or cyclic C₁-C₁₂ alkoxy group, C₆-C₂₀ aryl group, orC₇-C₁₂ aralkyl or aryloxyalkyl group, R⁵ is an optionally substitutedphenyl group having the formula (A-2) below or an optionally substitutedethynyl group having the formula (A-3) below, m is an integer of 1 to 4,n is an integer of 0 to 3, and p is an integer of 0 to 5.

Herein R⁶ and R⁷ are each independently hydrogen or a straight, branchedor cyclic C₁-C₆ alkyl group, R⁶ and R⁷ may bond together to form a ringwith the nitrogen atom to which they are attached, which ring maycontain an ether bond; R⁸ is hydroxyl, halogen, trifluoromethyl, nitro,carboxyl, a C₂-C₁₀ acyl group, C₂-C₁₀ acyloxy group, C₂-C₁₀alkoxycarbonyl group, a straight, branched or cyclic C₁-C₁₂ alkyl groupwhich may contain oxo, a straight, branched or cyclic C₂-C₁₂ alkenylgroup which may contain oxo, a straight, branched or cyclic C₁-C₁₂alkoxy group, C₆-C₂₀ aryl group, or C₇-C₁₂ aralkyl or aryloxyalkylgroup; R⁹ is hydrogen, hydroxyl, halogen, trifluoromethyl, nitro,carboxyl, a C₂-C₁₀ acyl group, C₂-C₁₀ acyloxy group, C₂-C₁₀alkoxycarbonyl group, a straight, branched or cyclic C₁-C₁₂ alkyl groupwhich may contain oxo, a straight, branched or cyclic C₂-C₁₂ alkenylgroup which may contain oxo, a straight, branched or cyclic C₁-C₁₂alkoxy group, C₆-C₂₀ aryl group, or C₇-C₁₂ aralkyl or aryloxyalkylgroup, and q is an integer of 0 to 5.

The resist composition may further comprise an acid generator capable ofgenerating a sulfonic acid, imide acid or methide acid and an organicsolvent.

In a preferred embodiment, the base polymer comprises recurring unitshaving the formula (a1) or recurring units having the formula (a2):

wherein R^(A) is each independently hydrogen or methyl, X¹ is a singlebond, phenylene group, naphthylene group, or C₁-C₁₂ linking groupcontaining an ester moiety and/or lactone ring, X² is a single bond orester group, R¹¹ and R¹² each are an acid labile group.

The resist composition may further comprise a dissolution inhibitor.

In one embodiment, the resist composition is a chemically amplifiedpositive resist composition.

In another embodiment, the base polymer is free of an acid labile group.The resist composition may further comprise a crosslinker. The resistcomposition is typically a chemically amplified negative resistcomposition.

In a preferred embodiment, the base polymer further comprises recurringunits of at least one type selected from the formulae (f1) to (f3).

Herein R^(A) is each independently hydrogen or methyl; Z¹ is a singlebond, phenylene group, —O—Z¹¹— or —C(═O)—Z¹²—Z¹¹—, Z¹¹ is a straight,branched or cyclic C₁-C₆ alkylene or C₂-C₆ alkenylene group which maycontain a carbonyl, ester, ether or hydroxy moiety, or phenylene groupZ¹² is —O— or —NH—; R²¹, R²², R²³, R²⁴, R²⁵, R²⁶, R²⁷ and R²⁸ are eachindependently a straight, branched or cyclic C₁-C₁₂ alkyl group whichmay contain a carbonyl, ester or ether moiety, or C₆-C₁₂ aryl group orC₇-C₂₀ aralkyl group, in which at least one hydrogen may be substitutedby a C₁-C₁₀ straight, branched or cyclic alkyl moiety, halogen,trifluoromethyl, cyano, nitro, hydroxyl, mercapto, C₁-C₁₀ straight,branched or cyclic alkoxy moiety, C₂-C₁₀ straight, branched or cyclicalkoxycarbonyl moiety, or C₂-C₁₀ straight, branched or cyclic acyloxymoiety, R²³ and R²⁴, or R²⁶ and R²⁷ may bond together directly or via amethylene moiety or ether bond to form a ring with the sulfur atom towhich they are attached; Z² is a single bond, —Z²¹—C(═O)—O—, —Z²¹—O— or—Z²¹—O—C(═O)—, Z²¹ is a straight, branched or cyclic C₁-C₁₂ alkylenegroup which may contain a carbonyl, ester or ether moiety; Z³ is asingle bond, methylene group, ethylene group, phenylene group,fluorinated phenylene group, —O—Z³¹—, or —C(═O)—Z³²—Z³¹—, Z³¹ is astraight, branched or cyclic C₁-C₆ alkylene group or C₂-C₆ alkenylenegroup which may contain a carbonyl, ester, ether, fluorine or hydroxylmoiety, or a phenylene, fluorinated phenylene ortrifluoromethyl-substituted phenylene group, Z³² is —O— or —NH—; A¹ ishydrogen or trifluoromethyl; and M⁻ is a non-nucleophilic counter ion.

The resist composition may further comprise a surfactant.

In another aspect, the invention provides a process for forming apattern comprising the steps of applying the resist composition definedabove onto a substrate, baking to form a resist film, exposing theresist film to high-energy radiation, and developing the exposed film ina developer.

In a preferred embodiment, the high-energy radiation is ArF excimerlaser radiation of wavelength 193 nm, KrF excimer laser radiation ofwavelength 248 nm, EB, or EUV of wavelength 3 to 15 nm.

Advantageous Effects of Invention

A resist film containing an iodonium salt of fluorinated aminobenzoicacid, fluorinated nitrobenzoic acid or fluorinated hydroxybenzoic acidhas a high dissolution contrast, and offers an improved resolution andwide focus margin as positive and negative resist films subject toalkaline development and as a negative resist film subject to organicsolvent development. Since the iodonium salt is fully dispersible in theresist film, the resist film also has the advantage of reduced LWR.

DESCRIPTION OF EMBODIMENTS

As used herein, the singular forms “a,” “an” and “the” include pluralreferents unless the context clearly dictates otherwise. The notation(C_(n)-C_(m)) means a group containing from n to m carbon atoms pergroup. In chemical formulae, Me stands for methyl, Ac for acetyl, and Phfor phenyl.

The abbreviations and acronyms have the following meaning.

EB: electron beam

EUV: extreme ultraviolet

Mw: weight average molecular weight

Mn: number average molecular weight

Mw/Mn: molecular weight distribution or dispersity

GPC: gel permeation chromatography

PEB: post-exposure bake

PAG: photoacid generator

LWR: line width roughness

CDU: critical dimension uniformity

Resist Composition

The resist composition of the invention is defined as comprising a basepolymer and a quencher containing an iodonium salt of fluorinatedaminobenzoic acid, fluorinated nitrobenzoic acid or fluorinatedhydroxybenzoic acid. The iodonium salt is an acid generator capable ofgenerating fluorinated aminobenzoic acid, fluorinated nitrobenzoic acidor fluorinated hydroxybenzoic acid upon light exposure, but alsofunctions as a quencher at the same time because it possesses a weaklybasic amino or nitro group and a strongly basic iodonium. Since thefluorinated aminobenzoic acid, fluorinated nitrobenzoic acid orfluorinated hydroxybenzoic acid does not possess a sufficient acidity toinduce deprotection reaction of acid labile groups, it is recommended toseparately add an acid generator capable of generating a strong acidsuch as α-fluorinated sulfonic acid, imide acid or methide acid, as willbe described later, in order to induce deprotection reaction of acidlabile groups. The acid generator capable of generating a strong acidsuch as α-fluorinated sulfonic acid, imide acid or methide acid may beeither of separate type which is added to the base polymer or of boundtype which is bound in the base polymer.

When a resist composition containing the iodonium salt of fluorinatedaminobenzoic acid, fluorinated nitrobenzoic acid or fluorinatedhydroxybenzoic acid in admixture with an acid generator capable ofgenerating a perfluoroalkylsulfonic acid or superstrong acid is exposedto radiation, fluorinated aminobenzoic acid, fluorinated nitrobenzoicacid or fluorinated hydroxybenzoic acid and perfluoroalkylsulfonic acidgenerate. Since the acid generator is not entirely decomposed, theundecomposed acid generator is present nearby. When the iodonium saltcapable of generating fluorinated aminobenzoic acid, fluorinatednitrobenzoic acid or fluorinated hydroxybenzoic acid co-exists with theperfluoroalkylsulfonic acid, the perfluoroalkylsulfonic acid firstadsorbs to the amino, nitro or hydroxy group on the fluorinatedaminobenzoic acid, fluorinated nitrobenzoic acid or fluorinatedhydroxybenzoic acid and then undergoes ion exchange, whereby an iodoniumsalt of perfluoroalkylsulfonic acid is created and a fluorinatedaminobenzoic acid, fluorinated nitrobenzoic acid or fluorinatedhydroxybenzoic acid is released. This is because the salt ofperfluoroalkylsulfonic acid having a high acid strength is more stable.In contrast, when an iodonium salt of perfluoroalkylsulfonic acidco-exists with a fluorinated aminobenzoic acid, fluorinated nitrobenzoicacid or fluorinated hydroxybenzoic acid, no ion exchange takes place.The ion exchange reaction according to the acid strength series occursnot only with iodonium salts, but also similarly with sulfonium salts.Likewise, ion exchange takes place not only with theperfluoroalkylsulfonic acid, but also similarly with arylsulfonic acid,alkylsulfonic acid, imide acid and methide acid having a higher acidstrength than the fluorinated aminobenzoic acid, fluorinatednitrobenzoic acid or fluorinated hydroxybenzoic acid. The iodonium saltdefined herein has a high acid adsorptivity owing to the amino or nitrogroup contained therein, and is characterized by a higher quenchercapability than any iodonium salts of fluorobenzoic acid free of anamino or nitro group.

While the quencher used herein should essentially contain the iodoniumsalt of fluorinated aminobenzoic acid, fluorinated nitrobenzoic acid orfluorinated hydroxybenzoic acid, another sulfonium or iodonium salt maybe separately added as the quencher. Examples of the sulfonium oriodonium salt to be added as the quencher include sulfonium or iodoniumsalts of carboxylic acid, sulfonic acid, imide acid and saccharin. Thecarboxylic acid used herein may or may not be fluorinated at α-position.

For the LWR improving purpose, it is effective to prevent a polymerand/or acid generator from agglomeration as indicated above. Effectivemeans for preventing agglomeration of a polymer is by reducing thedifference between hydrophobic and hydrophilic properties or by loweringthe glass transition temperature (Tg) thereof. Specifically, it iseffective to reduce the polarity difference between a hydrophobic acidlabile group and a hydrophilic adhesive group or to lower the Tg byusing a compact adhesive group like monocyclic lactone. One effectivemeans for preventing agglomeration of an acid generator is byintroducing a substituent into the triphenylsulfonium cation. Inparticular, with respect to a methacrylate polymer containing analicyclic protective group and a lactone adhesive group for ArFlithography, a triphenylsulfonium composed solely of aromatic groups hasa heterogeneous structure and low compatibility. As the substituent tobe introduced into triphenylsulfonium, an alicyclic group or lactonesimilar to those used in the base polymer is regarded adequate. Whenlactone is introduced in a sulfonium salt which is hydrophilic, theresulting sulfonium salt becomes too hydrophilic and thus lesscompatible with a polymer, with a likelihood that the sulfonium saltwill agglomerate. When a hydrophobic alkyl group is introduced, thesulfonium salt may be uniformly dispersed within the resist film. WO2011/048919 discloses the technique for improving LWR by introducing analkyl group into a sulfonium salt capable of generating an α-fluorinatedsulfone imide acid.

As alluded to previously, the iodonium salt type quencher is moresoluble in solvents than the sulfonium salt type quencher. Therefore,the iodonium salt type quencher is more dispersible in a resist solutionand more dispersible in a resist film, leading to improvements in LWRand CDU. This holds true not only in the case of quencher, but also inthe case of acid generator. Like the quencher, the acid generator ofiodonium salt type is fully dispersible in a resist film and has lowacid diffusion, leading to improvements in LWR and CDU.

The iodonium salt of fluorinated aminobenzoic acid, fluorinatednitrobenzoic acid or fluorinated hydroxybenzoic acid exerts a contrastenhancing effect, which may stand good either in positive and negativetone pattern formation by alkaline development or in negative tonepattern formation by organic solvent development.

Quencher

The quencher used herein contain an iodonium salt having the formula(A).

In formula (A), R¹ is a nitro group, hydroxyl group or a group havingthe formula (A-1) below. R² is fluorine or trifluoromethyl. R³ is methylor cyano. R⁴ is hydroxyl, halogen, trifluoromethyl, nitro, carboxyl, aC₂-C₁₀ acyl group, a C₂-C₁₀ acyloxy group, a C₂-C₁₀ alkoxycarbonylgroup, a straight, branched or cyclic C₁-C₁₂ alkyl group which maycontain oxo, a straight, branched or cyclic C₂-C₁₂ alkenyl group whichmay contain oxo, a straight, branched or cyclic C₁-C₁₂ alkoxy group, aC₆-C₂₀ aryl group, or a C₇-C₁₂ aralkyl or aryloxyalkyl group. R⁵ is anoptionally substituted phenyl group having the formula (A-2) below or anoptionally substituted ethynyl group having the formula (A-3) below, mis an integer of 1 to 4, n is an integer of 0 to 3, and p is an integerof 0 to 5.

In formula (A-1), R⁶ and R⁷ are each independently hydrogen or astraight, branched or cyclic C₁-C₆ alkyl group, R⁶ and R⁷ may bondtogether to form a ring with the nitrogen atom to which they areattached, which ring may contain an ether bond.

In formula (A-2), R⁸ is hydroxyl, halogen, trifluoromethyl, nitro,carboxyl, a C₂-C₁₀ acyl group, a C₂-C₁₀ acyloxy group, a C₂-C₁₀alkoxycarbonyl group, a straight, branched or cyclic C₁-C₁₂ alkyl groupwhich may contain oxo, a straight, branched or cyclic C₂-C₁₂ alkenylgroup which may contain oxo, a straight, branched or cyclic C₁-C₁₂alkoxy group, a C₆-C₂₀ aryl group, or a C₇-C₁₂ aralkyl or aryloxyalkylgroup.

In formula (A-3), R⁹ is hydrogen, hydroxyl, halogen, trifluoromethyl,nitro, carboxyl, a C₂-C₁₀ acyl group, a C₂-C₁₀ acyloxy group, a C₂-C₁₀alkoxycarbonyl group, a straight, branched or cyclic C₁-C₁₂ alkyl groupwhich may contain oxo, a straight, branched or cyclic C₂-C₁₂ alkenylgroup which may contain oxo, a straight, branched or cyclic C₁-C₁₂alkoxy group, a C₆-C₂₀ aryl group, or a C₇-C₁₂ aralkyl or aryloxyalkylgroup, and q is an integer of 0 to 5.

Examples of the cation moiety in the iodonium salt having formula (A)are given below, but not limited thereto.

Examples of the anion moiety in the iodonium salt having formula (A) aregiven below, but not limited thereto.

The iodonium salt of fluorinated aminobenzoic acid, fluorinatednitrobenzoic acid or fluorinated hydroxybenzoic acid having formula (A)may be synthesized, for example, by ion exchange with an iodonium saltof weaker acid than the fluorinated aminobenzoic acid, fluorinatednitrobenzoic acid or fluorinated hydroxybenzoic acid. Examples of theweaker acid than the fluorinated aminobenzoic acid, fluorinatednitrobenzoic acid or fluorinated hydroxybenzoic acid includehydrochloric acid, non-fluorinated carboxylic acids, and carbonic acid.Alternatively, the iodonium salt may be synthesized by ion exchange of asodium salt of a fluorinated aminobenzoic acid, fluorinated nitrobenzoicacid or fluorinated hydroxybenzoic acid with an iodonium chloride.

In the resist composition, the iodonium salt having formula (A) ispreferably used in an amount of 0.001 to 50 parts, more preferably 0.01to 20 parts by weight per 100 parts by weight of the base polymer, asviewed from sensitivity and acid diffusion suppressing effect.

Base Polymer

Where the resist composition is of positive tone, the base polymercomprises recurring units containing an acid labile group, preferablyrecurring units having the formula (a1) or recurring units having theformula (a2). These units are simply referred to as recurring units (a1)and (a2).

Herein R^(A) is each independently hydrogen or methyl. X¹ is a singlebond, phenylene group, naphthylene group, or a C₁-C₁₂ linking groupcontaining an ester moiety and/or lactone ring. X² is a single bond orester group. R¹¹ and R¹² each are an acid labile group.

Examples of the recurring units (a1) are shown below, but not limitedthereto. R^(A) and R¹¹ are as defined above.

The acid labile groups represented by R¹¹ and R¹² in the recurring units(a1) and (a2) may be selected from a variety of such groups, forexample, those groups described in JP-A 2013-080033 (U.S. Pat. No.8,574,817) and JP-A 2013-083821 (U.S. Pat. No. 8,846,303).

Typical of the acid labile group are groups of the following formulae(AL-1) to (AL-3).

In formulae (AL-1) and (AL-2), R¹³ and R¹⁶ are each independently amonovalent hydrocarbon group of 1 to 40 carbon atoms, preferably 1 to 20carbon atoms, typically straight, branched or cyclic alkyl, which maycontain a heteroatom such as oxygen, sulfur, nitrogen or fluorine. R¹⁴and R¹⁵ are each independently hydrogen or a monovalent hydrocarbongroup of 1 to 20 carbon atoms, typically straight, branched or cyclicalkyl, which may contain a heteroatom such as oxygen, sulfur, nitrogenor fluorine. Al is an integer of 0 to 10, especially 1 to 5. A pair ofR¹⁴ and R¹⁵, R¹⁴ and R¹⁶, or R¹⁵ and R¹⁶ may bond together to form aring, typically alicyclic, with the carbon atom or carbon and oxygenatoms to which they are attached, the ring containing 3 to 20 carbonatoms, preferably 4 to 16 carbon atoms.

In formula (AL-3), R¹⁷, R¹⁸ and R¹⁹ are each independently a monovalenthydrocarbon group of 1 to 20 carbon atoms, typically straight, branchedor cyclic alkyl, which may contain a heteroatom such as oxygen, sulfur,nitrogen or fluorine. A pair of R¹⁷ and R¹⁸, R¹⁷ and R¹⁹, or R¹⁸ and R¹⁹may bond together to form a ring, typically alicyclic, with the carbonatom to which they are attached, the ring containing 3 to 20 carbonatoms, preferably 4 to 16 carbon atoms.

The base polymer may further comprise recurring units (b) having aphenolic hydroxyl group as an adhesive group. Examples of suitablemonomers from which recurring units (b) are derived are given below, butnot limited thereto. Herein R^(A) is as defined above.

Further, recurring units (c) having another adhesive group selected fromhydroxyl (other than the foregoing phenolic hydroxyl), lactone ring,ether, ester, carbonyl and cyano groups may also be incorporated in thebase polymer. Examples of suitable monomers from which recurring units(c) are derived are given below, but not limited thereto. Herein R^(A)is as defined above.

In the case of a monomer having a hydroxyl group, the hydroxyl group maybe replaced by an acetal group susceptible to deprotection with acid,typically ethoxyethoxy, prior to polymerization, and the polymerizationbe followed by deprotection with weak acid and water. Alternatively, thehydroxyl group may be replaced by an acetyl, formyl, pivaloyl or similargroup prior to polymerization, and the polymerization be followed byalkaline hydrolysis.

In another preferred embodiment, the base polymer may further compriserecurring units (d) selected from units of indene, benzofuran,benzothiophene, acenaphthylene, chromone, coumarin, and norbornadiene,or derivatives thereof. Suitable monomers are exemplified below.

Besides the recurring units described above, further recurring units (e)may be incorporated in the base polymer, examples of which includestyrene, vinylnaphthalene, vinylanthracene, vinylpyrene,methyleneindene, vinylpyridine, and vinylcarbazole.

In a further embodiment, recurring units (f) derived from an onium salthaving a polymerizable carbon-carbon double bond may be incorporated inthe base polymer. JP-A 2005-084365 discloses sulfonium and iodoniumsalts having a polymerizable carbon-carbon double bond capable ofgenerating a sulfonic acid. JP-A 2006-178317 discloses a sulfonium salthaving sulfonic acid directly attached to the main chain.

In a preferred embodiment, the base polymer may further compriserecurring units (f) of at least one type selected from formulae (f1),(f2) and (f3). These units are simply referred to as recurring units(f1), (f2) and (f3), which may be used alone or in combination of two ormore types.

Herein R^(A) is each independently hydrogen or methyl. Z¹ is a singlebond, phenylene group, —O—Z¹¹—, or —C(═O)—Z¹²—Z¹¹—, wherein Z¹¹ is astraight, branched or cyclic C₁-C₆ alkylene group or C₂-C₆ alkenylenegroup which may contain a carbonyl, ester, ether or hydroxyl moiety, ora phenylene group, and Z¹² is —O— or —NH—.

R²¹, R²², R²³, R²⁴, R²⁵, R²⁶, R²⁷, and R²⁸ are each independently astraight, branched or cyclic C₁-C₁₂ alkyl group which may contain acarbonyl, ester or ether moiety, or a C₆-C₁₂ aryl group or C₇-C₂₀aralkyl group, in which at least one hydrogen (i.e., one or more or evenall hydrogen atoms) may be substituted by a C₁-C₁₀ straight, branched orcyclic alkyl moiety, halogen, trifluoromethyl, cyano, nitro, hydroxyl,mercapto, C₁-C₁₀ straight, branched or cyclic alkoxy moiety, C₂-C₁₀straight, branched or cyclic alkoxycarbonyl moiety, or C₂-C₁₀ straight,branched or cyclic acyloxy moiety. Also, a pair of R²³ and R²⁴, or R²⁶and R²⁷ may bond together directly or via a methylene moiety or etherbond to form a ring with the sulfur atom to which they are attached.

Z² is a single bond, —Z²¹—C(═O)—O—, —Z²¹—O— or —Z²¹—O—C(═O)—, whereinZ²¹ is a straight, branched or cyclic C₁-C₁₂ alkylene group which maycontain a carbonyl, ester or ether moiety.

Z³ is a single bond, methylene group, ethylene group, phenylene group,fluorinated phenylene group, —O—Z³¹—, or —C(═O)—Z³²—Z³¹—, wherein Z³¹ isa straight, branched or cyclic C₁-C₆ alkylene group or C₂-C₆ alkenylenegroup which may contain a carbonyl, ester, ether, fluorine or hydroxylmoiety, or a phenylene, fluorinated phenylene ortrifluoromethyl-substituted phenylene group, and Z³² is —O— or —NH—.

A¹ is hydrogen or trifluoromethyl, and M⁻ is a non-nucleophilic counterion.

Examples of the monomer from which recurring unit (f1) is derived areshown below, but not limited thereto. R^(A) and M⁻ are as defined above.

Examples of the non-nucleophilic counter ion M⁻ include halide ions suchas chloride and bromide ions; fluoroalkylsulfonate ions such astriflate, 1,1,1-trifluoroethanesulfonate, and nonafluorobutanesulfonate;arylsulfonate ions such as tosylate, benzenesulfonate,4-fluorobenzenesulfonate, and 1,2,3,4,5-pentafluorobenzenesulfonate;alkylsulfonate ions such as mesylate and butanesulfonate; imidates suchas bis(trifluoromethylsulfonyl)imide, bis(perfluoroethylsulfonyl)imideand bis(perfluorobutylsulfonyl)imide; methidates such astris(trifluoromethylsulfonyl)methide andtris(perfluoroethylsulfonyl)methide.

Also included are sulfonates having fluorine substituted at α-positionas represented by the formula (K-1) and sulfonates having fluorinesubstituted at α- and β-positions as represented by the formula (K-2).

In formula (K-1), R³¹ is hydrogen, or a C₁-C₂₀ straight, branched orcyclic alkyl group, C₂-C₂₀ straight, branched or cyclic alkenyl group,or C₆-C₂₀ aryl group, which may contain an ether, ester, carbonylmoiety, lactone ring, or fluorine atom. In formula (K-2), R³² ishydrogen, or a C₁-C₃₀ straight, branched or cyclic alkyl group, C₂-C₃₀straight, branched or cyclic acyl group, C₂-C₂₀ straight, branched orcyclic alkenyl group, C₆-C₂₀ aryl group or C₆-C₂₀ aryloxy group, whichmay contain an ether, ester, carbonyl moiety or lactone ring.

Examples of the monomer from which recurring unit (f2) is derived areshown below, but not limited thereto. R^(A) is as defined above.

Examples of the monomer from which recurring unit (f3) is derived areshown below, but not limited thereto. R^(A) is as defined above.

The attachment of an acid generator to the polymer main chain iseffective in restraining acid diffusion, thereby preventing a reductionof resolution due to blur by acid diffusion. Also edge roughness isimproved since the acid generator is uniformly distributed. Where a basepolymer containing recurring units (f) is used, the addition of aseparate PAG may be omitted.

The base polymer for formulating the positive resist compositioncomprises recurring units (a1) or (a2) having an acid labile group asessential component and additional recurring units (b), (c), (d), (e),and (f) as optional components. A fraction of units (a1), (a2), (b),(c), (d), (e), and (f) is: preferably 0≤a1<1.0, 0≤a2<1.0, 0<a1+a2<1.0,0≤b≤0.9, 0≤c≤0.9, 0≤d≤0.8, 0≤e≤0.8, 0≤f1≤0.5, 0≤f2≤0.5, and 0≤f3≤0.5;more preferably 0≤a1≤0.9, 0≤a2≤0.9, 0.1≤a1+a2≤0.9, 0≤b≤0.8, 0≤c≤0.8,0≤d≤0.7, 0≤e≥0.7, 0≤f1≤0.4, 0≤f2≤0.4, and 0≤f3≤0.4; and even morepreferably 0≤a1≤0.8, 0≤a2≤0.8, 0.1≤a1+a2≤0.8, 0≤b≤0.75, 0≤c≤0.75,0≤d≤0.6, 0≤e≤0.6, 0≤f1≤0.3, 0≤f2≤0.3, and 0≤f3≤0.3. Notably,a1+a2+b+c+d+e+f1+f2+f3=1.0.

For the base polymer for formulating the negative resist composition, anacid labile group is not necessarily essential. The base polymercomprises recurring units (b), and optionally recurring units (c), (d),(e), and/or (f). A fraction of these units is: preferably <b≤1.0,0≤c≤0.9, 0≤d≤0.8, 0≤e≤0.8, 0≤f1≤0.5, 0≤f2≤0.5, and 0≤f3≤0.5; morepreferably 0.2≤b≤1.0, 0≤c≤0.8, 0≤d≤0.7, 0≤e≤0.7, 0≤f1≤0.4, 0≤f2≤0.4, and0≤f3≤0.4; and even more preferably 0.3≤b≤1.0, 0≤c≤0.75, 0≤d≤0.6,0≤e≤0.6, 0≤f1≤0.3, 0≤f2≤0.3, and 0≤f3≤0.3. Notably,b+c+d+e+f1+f2+f3=1.0.

The base polymer may be synthesized by any desired methods, for example,by dissolving one or more monomers selected from the monomerscorresponding to the foregoing recurring units in an organic solvent,adding a radical polymerization initiator thereto, and effecting heatpolymerization. Examples of the organic solvent which can be used forpolymerization include toluene, benzene, tetrahydrofuran, diethyl ether,and dioxane. Examples of the polymerization initiator used hereininclude 2,2′-azobisisobutyronitrile (AIBN),2,2′-azobis(2,4-dimethylvaleronitrile), dimethyl2,2-azobis(2-methylpropionate), benzoyl peroxide, and lauroyl peroxide.Preferably the system is heated at 50 to 80° C. for polymerization totake place. The reaction time is 2 to 100 hours, preferably 5 to 20hours.

When hydroxystyrene or hydroxyvinylnaphthalene is copolymerized, analternative method is possible. Specifically, acetoxystyrene oracetoxyvinylnaphthalene is used instead of hydroxystyrene orhydroxyvinylnaphthalene, and after polymerization, the acetoxy group isdeprotected by alkaline hydrolysis, for thereby converting the polymerproduct to hydroxystyrene or hydroxyvinylnaphthalene. For alkalinehydrolysis, a base such as aqueous ammonia or triethylamine may be used.Preferably the reaction temperature is −20° C. to 100° C., morepreferably 0° C. to 60° C., and the reaction time is 0.2 to 100 hours,more preferably 0.5 to 20 hours.

The base polymer should preferably have a weight average molecularweight (Mw) in the range of 1,000 to 500,000, and more preferably 2,000to 30,000, as measured by GPC versus polystyrene standards usingtetrahydrofuran (THF) solvent. With too low a Mw, the resist compositionmay become less heat resistant. A polymer with too high a Mw may losealkaline solubility and give rise to a footing phenomenon after patternformation.

If a base polymer has a wide molecular weight distribution or dispersity(Mw/Mn), which indicates the presence of lower and higher molecularweight polymer fractions, there is a possibility that foreign matter isleft on the pattern or the pattern profile is degraded. The influencesof molecular weight and dispersity become stronger as the pattern rulebecomes finer. Therefore, the base polymer should preferably have anarrow dispersity (Mw/Mn) of 1.0 to 2.0, especially 1.0 to 1.5, in orderto provide a resist composition suitable for micropatterning to a smallfeature size.

It is understood that a blend of two or more polymers which differ incompositional ratio, Mw or Mw/Mn is acceptable.

Acid Generator

To the resist composition comprising the base polymer and the iodoniumsalt having formula (A), an acid generator may be added so that thecomposition may function as a chemically amplified positive or negativeresist composition. The acid generator is typically a compound (PAG)capable of generating an acid upon exposure to actinic ray or radiation.Although the PAG used herein may be any compound capable of generatingan acid upon exposure to high-energy radiation, those compounds capableof generating sulfonic acid, imide acid (imidic acid) or methide acidare preferred. Suitable PAGs include sulfonium salts, iodonium salts,sulfonyldiazomethane, N-sulfonyloxyimide, and oxime-O-sulfonate acidgenerators. Exemplary PAGs are described in JP-A 2008-111103, paragraphs[0122]-[0142] (U.S. Pat. No. 7,537,880).

As the PAG used herein, those having the formula (1) are preferred.

In formula (1), R¹⁰¹, R¹⁰² and R¹⁰³ are each independently a C₁-C₂₀straight, branched or cyclic monovalent hydrocarbon group which maycontain a heteroatom. Any two of R¹⁰¹, R¹⁰² and R¹⁰³ may bond togetherto form a ring with the sulfur atom to which they are attached.

In formula (1), X⁻ is an anion of the following formula (1A), (1B), (1C)or (1D).

In formula (1A), R^(fa) is fluorine or a C₁-C₄₀ straight, branched orcyclic monovalent hydrocarbon group which may contain a heteroatom.

Of the anions of formula (1A), an anion having the formula (1A′) ispreferred.

In formula (1A′), R¹⁰⁴ is hydrogen or trifluoromethyl, preferablytrifluoromethyl. R¹⁰⁵ is a C₁-C₃₈ straight, branched or cyclicmonovalent hydrocarbon group which may contain a heteroatom. As theheteroatom, oxygen, nitrogen, sulfur and halogen atoms are preferred,with oxygen being most preferred. Of the monovalent hydrocarbon groupsrepresented by R¹⁰⁵, those groups of 6 to 30 carbon atoms are preferredfrom the aspect of achieving a high resolution in forming patterns offine feature size. Suitable monovalent hydrocarbon groups include, butare not limited to, methyl, ethyl, propyl, isopropyl, butyl, isobutyl,s-butyl, t-butyl, pentyl, neopentyl, cyclopentyl, hexyl, cyclohexyl,3-cyclohexenyl, heptyl, 2-ethylhexyl, nonyl, undecyl, tridecyl,pentadecyl, heptadecyl, 1-adamantyl, 2-adamantyl, 1-adamantylmethyl,norbornyl, norbornylmethyl, tricyclodecanyl, tetracyclododecanyl,tetracyclododecanylmethyl, dicyclohexylmethyl, eicosanyl, allyl, benzyl,diphenylmethyl, tetrahydrofuryl, methoxymethyl, ethoxymethyl,methylthiomethyl, acetamidomethyl, trifluoroethyl,(2-methoxyethoxy)methyl, acetoxymethyl, 2-carboxy-1-cyclohexyl,2-oxopropyl, 4-oxo-1-adamantyl, and 3-oxocyclohexyl. In these groups,one or more hydrogen atoms may be substituted by a moiety containing aheteroatom such as oxygen, sulfur, nitrogen or halogen, or a moietycontaining a heteroatom such as oxygen, sulfur or nitrogen may intervenebetween carbon atoms, so that the group may contain a hydroxyl, cyano,carbonyl, ether, ester, sulfonic acid ester, carbonate, lactone ring,sultone ring, carboxylic anhydride or haloalkyl moiety.

With respect to the synthesis of the sulfonium salt having an anion offormula (1A′), reference may be made to JP-A 2007-145797, JP-A2008-106045, JP-A 2009-007327, and JP-A 2009-258695. Also useful are thesulfonium salts described in JP-A 2010-215608, JP-A 2012-041320, JP-A2012-106986, and JP-A 2012-153644.

Examples of the sulfonium salt having an anion of formula (1A) are shownbelow, but not limited thereto.

In formula (1B), R^(fb1) and R^(fb2) are each independently fluorine ora C₁-C₄₀ straight, branched or cyclic monovalent hydrocarbon group whichmay contain a heteroatom. Illustrative examples of the monovalenthydrocarbon group are as exemplified for R¹⁰⁵. Preferably R^(fb1) andR^(fb2) are fluorine or C₁-C₄ straight fluorinated alkyl groups. Also,R^(fb1) and R^(fb2) may bond together to form a ring with the linkage:—CF₂—SO₂—N⁻—SO₂—CF₂— to which they are attached. It is preferred to forma ring structure via a fluorinated ethylene or fluorinated propylenegroup.

In formula (1C), R^(fc1), R^(fc2) and R^(fc3) are each independentlyfluorine or a C₁-C₄₀ straight, branched or cyclic monovalent hydrocarbongroup which may contain a heteroatom. Illustrative examples of themonovalent hydrocarbon group are as exemplified for R¹⁰⁵. PreferablyR^(fc1), R^(fc2) and R^(fcc3) are fluorine or C₁-C₄ straight fluorinatedalkyl groups. Also, R^(fc1) and R^(fc2) may bond together to form a ringwith the linkage: —CF₂—SO₂—C⁻—SO₂—CF₂— to which they are attached. It ispreferred to form a ring structure via a fluorinated ethylene orfluorinated propylene group.

In formula (1D), R^(fd) is a C₁-C₄₀ straight, branched or cyclicmonovalent hydrocarbon group which may contain a heteroatom.Illustrative examples of the monovalent hydrocarbon group are asexemplified for R¹⁰⁵.

With respect to the synthesis of the sulfonium salt having an anion offormula (1D), reference may be made to JP-A 2010-215608 and JP-A2014-133723.

Examples of the sulfonium salt having an anion of formula (1D) are shownbelow, but not limited thereto.

Notably, the compound having the anion of formula (1D) does not havefluorine at the α-position relative to the sulfo group, but twotrifluoromethyl groups at the β-position. For this reason, it has asufficient acidity to sever the acid labile groups in the resistpolymer. Thus the compound is an effective PAG.

Another preferred PAG is a compound having the formula (2).

In formula (2), R²⁰¹ and R²⁰² are each independently a C₁-C₃₀ straight,branched or cyclic monovalent hydrocarbon group which may contain aheteroatom. R²⁰³ is a C₁-C₃₀ straight, branched or cyclic divalenthydrocarbon group which may contain a heteroatom. Any two of R²⁰¹, R²⁰²and R²⁰³ may bond together to form a ring with the sulfur atom to whichthey are attached. L^(A) is a single bond, ether bond or a C₁-C₂₀straight, branched or cyclic divalent hydrocarbon group which maycontain a heteroatom. X^(A), X^(B), X^(C) and X^(D) are eachindependently hydrogen, fluorine or trifluoromethyl, with the provisothat at least one of X^(A), X^(B), X^(C) and X^(D) is fluorine ortrifluoromethyl, and k is an integer of 0 to 3.

Examples of the monovalent hydrocarbon group include methyl, ethyl,propyl, isopropyl, n-butyl, s-butyl, t-butyl, n-pentyl, t-pentyl,n-hexyl, n-octyl, n-nonyl, n-decyl, cyclopentyl, cyclohexyl,2-ethylhexyl, cyclopentylmethyl, cyclopentylethyl, cyclopentylbutyl,cyclohexylmethyl, cyclohexylethyl, cyclohexylbutyl, norbornyl,oxanorbornyl, tricyclo[5.2.1.0^(2,6)]decanyl, adamantyl, phenyl,naphthyl and anthracenyl. In these groups, one or more hydrogen atomsmay be substituted by a heteroatom such as oxygen, sulfur, nitrogen orhalogen, or one or more carbon atoms may be substituted by a moietycontaining a heteroatom such as oxygen, sulfur or nitrogen, so that thegroup may contain a hydroxyl, cyano, carbonyl, ether, ester, sulfonicacid ester, carbonate, lactone ring, sultone ring, carboxylic anhydrideor haloalkyl moiety.

Suitable divalent hydrocarbon groups include straight alkane-diyl groupssuch as methylene, ethylene, propane-1,3-diyl, butane-1,4-diyl,pentane-1,5-diyl, hexane-1,6-diyl, heptane-1,7-diyl, octane-1,8-diyl,nonane-1,9-diyl, decane-1,10-diyl, undecane-1,11-diyl,dodecane-1,12-diyl, tridecane-1,13-diyl, tetradecane-1,14-diyl,pentadecane-1,15-diyl, hexadecane-1,16-diyl, and heptadecane-1,17-diyl;saturated cyclic divalent hydrocarbon groups such as cyclopentanediyl,cyclohexanediyl, norbornanediyl and adamantanediyl; and unsaturatedcyclic divalent hydrocarbon groups such as phenylene and naphthylene. Inthese groups, one or more hydrogen atom may be replaced by an alkylmoiety such as methyl, ethyl, propyl, n-butyl or t-butyl; one or morehydrogen atom may be replaced by a moiety containing a heteroatom suchas oxygen, sulfur, nitrogen or halogen; or a moiety containing aheteroatom such as oxygen, sulfur or nitrogen may intervene betweencarbon atoms, so that the group may contain a hydroxyl, cyano, carbonyl,ether, ester, sulfonic acid ester, carbonate, lactone ring, sultonering, carboxylic anhydride or haloalkyl moiety. Of the heteroatoms,oxygen is preferred.

Of the PAGs having formula (2), those having formula (2′) are preferred.

In formula (2′), L^(A) is as defined above. R is hydrogen ortrifluoromethyl, preferably trifluoromethyl. R³⁰¹, R³⁰² and R³⁰³ areeach independently hydrogen or a C₁-C₂₀ straight, branched or cyclicmonovalent hydrocarbon group which may contain a heteroatom. Suitablemonovalent hydrocarbon groups are as described above for R¹⁰⁵. Thesubscripts x and y are each independently an integer of 0 to 5, and z isan integer of 0 to 4.

Examples of the PAG having formula (2) are shown below, but not limitedthereto. Notably, R is as defined above.

Of the foregoing PAGs, those having an anion of formula (1A′) or (1D)are especially preferred because of reduced acid diffusion and highsolubility in the resist solvent. Also those having an anion of formula(2′) are especially preferred because of extremely reduced aciddiffusion.

The PAG is preferably added in an amount of 0.1 to 50 parts, and morepreferably 1 to 40 parts by weight per 100 parts by weight of the basepolymer.

Other Components

With the quencher containing the iodonium salt of formula (A), the basepolymer, and the acid generator, all defined above, other componentssuch as an organic solvent, surfactant, dissolution inhibitor, andcrosslinker may be blended in any desired combination to formulate achemically amplified positive or negative resist composition. Thispositive or negative resist composition has a very high sensitivity inthat the dissolution rate in developer of the base polymer in exposedareas is accelerated by catalytic reaction. In addition, the resist filmhas a high dissolution contrast, resolution, exposure latitude, andprocess adaptability, and provides a good pattern profile afterexposure, and minimal proximity bias because of restrained aciddiffusion. By virtue of these advantages, the composition is fullyuseful in commercial application and suited as a pattern-formingmaterial for the fabrication of VLSIs. Particularly when an acidgenerator is incorporated to formulate a chemically amplified positiveresist composition capable of utilizing acid catalyzed reaction, thecomposition has a higher sensitivity and is further improved in theproperties described above.

In the case of positive resist compositions, inclusion of a dissolutioninhibitor may lead to an increased difference in dissolution ratebetween exposed and unexposed areas and a further improvement inresolution. In the case of negative resist compositions, a negativepattern may be formed by adding a crosslinker to reduce the dissolutionrate of exposed area.

Examples of the organic solvent used herein are described in JP-A2008-111103, paragraphs [0144]-[0145] (U.S. Pat. No. 7,537,880).Exemplary solvents include ketones such as cyclohexanone, cyclopentanoneand methyl-2-n-pentyl ketone; alcohols such as 3-methoxybutanol,3-methyl-3-methoxybutanol, 1-methoxy-2-propanol, and1-ethoxy-2-propanol; ethers such as propylene glycol monomethyl ether,ethylene glycol monomethyl ether, propylene glycol monoethyl ether,ethylene glycol monoethyl ether, propylene glycol dimethyl ether, anddiethylene glycol dimethyl ether; esters such as propylene glycolmonomethyl ether acetate (PGMEA), propylene glycol monoethyl etheracetate, ethyl lactate, ethyl pyruvate, butyl acetate, methyl3-methoxypropionate, ethyl 3-ethoxypropionate, t-butyl acetate, t-butylpropionate, and propylene glycol mono-t-butyl ether acetate; andlactones such as γ-butyrolactone, which may be used alone or inadmixture.

The organic solvent is preferably added in an amount of 100 to 10,000parts, and more preferably 200 to 8,000 parts by weight per 100 parts byweight of the base polymer.

Exemplary surfactants are described in JP-A 2008-111103, paragraphs[0165]-[0166]. Inclusion of a surfactant may improve or control thecoating characteristics of the resist composition. The surfactant ispreferably added in an amount of 0.0001 to 10 parts by weight per 100parts by weight of the base polymer.

The dissolution inhibitor which can be used herein is a compound havingat least two phenolic hydroxyl groups on the molecule, in which anaverage of from 0 to 100 mol % of all the hydrogen atoms on the phenolichydroxyl groups are replaced by acid labile groups or a compound havingat least one carboxyl group on the molecule, in which an average of 50to 100 mol % of all the hydrogen atoms on the carboxyl groups arereplaced by acid labile groups, both the compounds having a molecularweight of 100 to 1,000, and preferably 150 to 800. Typical are bisphenolA, trisphenol, phenolphthalein, cresol novolac, naphthalenecarboxylicacid, adamantanecarboxylic acid, and cholic acid derivatives in whichthe hydrogen atom on the hydroxyl or carboxyl group is replaced by anacid labile group, as described in U.S. Pat. No. 7,771,914 (JP-A2008-122932, paragraphs [0155]-[0178]).

In the positive resist composition, the dissolution inhibitor ispreferably added in an amount of 0 to 50 parts, more preferably 5 to 40parts by weight per 100 parts by weight of the base polymer.

Suitable crosslinkers which can be used herein include epoxy compounds,melamine compounds, guanamine compounds, glycoluril compounds and ureacompounds having substituted thereon at least one group selected fromamong methylol, alkoxymethyl and acyloxymethyl groups, isocyanatecompounds, azide compounds, and compounds having a double bond such asan alkenyl ether group. These compounds may be used as an additive orintroduced into a polymer side chain as a pendant. Hydroxy-containingcompounds may also be used as the crosslinker.

Of the foregoing crosslinkers, examples of suitable epoxy compoundsinclude tris(2,3-epoxypropyl) isocyanurate, trimethylolmethanetriglycidyl ether, trimethylolpropane triglycidyl ether, andtriethylolethane triglycidyl ether. Examples of the melamine compoundinclude hexamethylol melamine, hexamethoxymethyl melamine, hexamethylolmelamine compounds having 1 to 6 methylol groups methoxymethylated andmixtures thereof, hexamethoxyethyl melamine, hexaacyloxymethyl melamine,hexamethylol melamine compounds having 1 to 6 methylol groupsacyloxymethylated and mixtures thereof. Examples of the guanaminecompound include tetramethylol guanamine, tetramethoxymethyl guanamine,tetramethylol guanamine compounds having 1 to 4 methylol groupsmethoxymethylated and mixtures thereof, tetramethoxyethyl guanamine,tetraacyloxyguanamine, tetramethylol guanamine compounds having 1 to 4methylol groups acyloxymethylated and mixtures thereof. Examples of theglycoluril compound include tetramethylol glycoluril,tetramethoxyglycoluril, tetramethoxymethyl glycoluril, tetramethylolglycoluril compounds having 1 to 4 methylol groups methoxymethylated andmixtures thereof, tetramethylol glycoluril compounds having 1 to 4methylol groups acyloxymethylated and mixtures thereof. Examples of theurea compound include tetramethylol urea, tetramethoxymethyl urea,tetramethylol urea compounds having 1 to 4 methylol groupsmethoxymethylated and mixtures thereof, and tetramethoxyethyl urea.

Suitable isocyanate compounds include tolylene diisocyanate,diphenylmethane diisocyanate, hexamethylene diisocyanate and cyclohexanediisocyanate. Suitable azide compounds include1,1′-biphenyl-4,4′-bisazide, 4,4′-methylidenebisazide, and4,4′-oxybisazide. Examples of the alkenyl ether group-containingcompound include ethylene glycol divinyl ether, triethylene glycoldivinyl ether, 1,2-propanediol divinyl ether, 1,4-butanediol divinylether, tetramethylene glycol divinyl ether, neopentyl glycol divinylether, trimethylol propane trivinyl ether, hexanediol divinyl ether,1,4-cyclohexanediol divinyl ether, pentaerythritol trivinyl ether,pentaerythritol tetravinyl ether, sorbitol tetravinyl ether, sorbitolpentavinyl ether, and trimethylol propane trivinyl ether.

In the negative resist composition, the crosslinker is preferably addedin an amount of 0.1 to 50 parts, more preferably 1 to 40 parts by weightper 100 parts by weight of the base polymer.

In the resist composition of the invention, a quencher other than theiodonium salt having formula (A) may be blended. The other quencher istypically selected from conventional basic compounds. Conventional basiccompounds include primary, secondary, and tertiary aliphatic amines,mixed amines, aromatic amines, heterocyclic amines, nitrogen-containingcompounds with carboxyl group, nitrogen-containing compounds withsulfonyl group, nitrogen-containing compounds with hydroxyl group,nitrogen-containing compounds with hydroxyphenyl group, alcoholicnitrogen-containing compounds, amide derivatives, imide derivatives, andcarbamate derivatives. Also included are primary, secondary, andtertiary amine compounds, specifically amine compounds having ahydroxyl, ether, ester, lactone ring, cyano, or sulfonic acid estergroup as described in JP-A 2008-111103, paragraphs [0146]-[0164], andcompounds having a carbamate group as described in JP 3790649. Additionof a basic compound may be effective for further suppressing thediffusion rate of acid in the resist film or correcting the patternprofile.

Onium salts such as sulfonium salts, iodonium salts and ammonium saltsof sulfonic acids which are not fluorinated at α-position as describedin U.S. Pat. No. 8,795,942 (JP-A 2008-158339) and similar onium salts ofcarboxylic acid may also be used as the other quencher. While anα-fluorinated sulfonic acid, imide acid, and methide acid are necessaryto deprotect the acid labile group of carboxylic acid ester, anα-non-fluorinated sulfonic acid and a carboxylic acid are released bysalt exchange with an α-non-fluorinated onium salt. An α-non-fluorinatedsulfonic acid and a carboxylic acid function as a quencher because theydo not induce deprotection reaction.

Also useful are quenchers of polymer type as described in U.S. Pat. No.7,598,016 (JP-A 2008-239918). The polymeric quencher segregates at theresist surface after coating and thus enhances the rectangularity ofresist pattern. When a protective film is applied as is often the casein the immersion lithography, the polymeric quencher is also effectivefor preventing a film thickness loss of resist pattern or rounding ofpattern top.

The other quencher is preferably added in an amount of 0 to 5 parts,more preferably 0 to 4 parts by weight per 100 parts by weight of thebase polymer.

To the resist composition, a polymeric additive (or water repellencyimprover) may also be added for improving the water repellency onsurface of a resist film as spin coated. The water repellency improvermay be used in the topcoatless immersion lithography. Suitable waterrepellency improvers include polymers having a fluoroalkyl group andpolymers having a specific structure with a1,1,1,3,3,3-hexafluoro-2-propanol residue and are described in JP-A2007-297590 and JP-A 2008-111103, for example. The water repellencyimprover to be added to the resist composition should be soluble in theorganic solvent as the developer. The water repellency improver ofspecific structure with a 1,1,1,3,3,3-hexafluoro-2-propanol residue iswell soluble in the developer. A polymer having an amino group or aminesalt copolymerized as recurring units may serve as the water repellentadditive and is effective for preventing evaporation of acid during PEB,thus preventing any hole pattern opening failure after development. Anappropriate amount of the water repellency improver is 0 to 20 parts,preferably 0.5 to 10 parts by weight per 100 parts by weight of the basepolymer.

Also, an acetylene alcohol may be blended in the resist composition.Suitable acetylene alcohols are described in JP-A 2008-122932,paragraphs [0179]-[0182]. An appropriate amount of the acetylene alcoholblended is 0 to 5 parts by weight per 100 parts by weight of the basepolymer.

Process

The resist composition is used in the fabrication of various integratedcircuits. Pattern formation using the resist composition may beperformed by well-known lithography processes. The process generallyinvolves coating, prebaking, exposure, and development. If necessary,any additional steps may be added.

For example, the positive resist composition is first applied onto asubstrate on which an integrated circuit is to be formed (e.g., Si,SiO₂, SiN, SiON, TiN, WSi, BPSG, SOG, or organic antireflective coating)or a substrate on which a mask circuit is to be formed (e.g., Cr, CrO,CrON, MoSi₂, or SiO₂) by a suitable coating technique such as spincoating, roll coating, flow coating, dipping, spraying or doctorcoating. The coating is prebaked on a hotplate at a temperature of 60 to150° C. for 10 seconds to 30 minutes, preferably 80 to 120° C. for 30seconds to 20 minutes. The resulting resist film is generally 0.1 to 2μm thick.

The resist film is then exposed to a desired pattern of high-energyradiation such as UV, deep-UV, EB, EUV, x-ray, soft x-ray, excimer laserlight, γ-ray or synchrotron radiation, directly or through a mask. Theexposure dose is preferably about 1 to 200 mJ/cm², more preferably about10 to 100 mJ/cm², or about 0.1 to 100 μC/cm², more preferably about 0.5to 50 μC/cm². The resist film is further baked (PEB) on a hotplate at 60to 150° C. for 10 seconds to 30 minutes, preferably 80 to 120° C. for 30seconds to 20 minutes.

Thereafter the resist film is developed with a developer in the form ofan aqueous base solution for 3 seconds to 3 minutes, preferably 5seconds to 2 minutes by conventional techniques such as dip, puddle andspray techniques. A typical developer is a 0.1 to 10 wt %, preferably 2to 5 wt % aqueous solution of tetramethylammonium hydroxide (TMAH),tetraethylammonium hydroxide (TEAH), tetrapropylammonium hydroxide(TPAH), or tetrabutylammonium hydroxide (TBAH). The resist film in theexposed area is dissolved in the developer whereas the resist film inthe unexposed area is not dissolved. In this way, the desired positivepattern is formed on the substrate. Inversely in the case of negativeresist, the exposed area of resist film is insolubilized and theunexposed area is dissolved in the developer. It is appreciated that theresist composition of the invention is best suited for micro-patterningusing such high-energy radiation as KrF and ArF excimer laser, EB, EUV,x-ray, soft x-ray, γ-ray and synchrotron radiation.

In an alternative embodiment, a negative pattern may be formed viaorganic solvent development using a positive resist compositioncomprising a base polymer having an acid labile group. The developerused herein is preferably selected from among 2-octanone, 2-nonanone,2-heptanone, 3-heptanone, 4-heptanone, 2-hexanone, 3-hexanone,diisobutyl ketone, methylcyclohexanone, acetophenone,methylacetophenone, propyl acetate, butyl acetate, isobutyl acetate,pentyl acetate, butenyl acetate, isopentyl acetate, propyl formate,butyl formate, isobutyl formate, pentyl formate, isopentyl formate,methyl valerate, methyl pentenoate, methyl crotonate, ethyl crotonate,methyl propionate, ethyl propionate, ethyl 3-ethoxypropionate, methyllactate, ethyl lactate, propyl lactate, butyl lactate, isobutyl lactate,pentyl lactate, isopentyl lactate, methyl 2-hydroxyisobutyrate, ethyl2-hydroxyisobutyrate, methyl benzoate, ethyl benzoate, phenyl acetate,benzyl acetate, methyl phenylacetate, benzyl formate, phenylethylformate, methyl 3-phenylpropionate, benzyl propionate, ethylphenylacetate, and 2-phenylethyl acetate, and mixtures thereof.

At the end of development, the resist film is rinsed. As the rinsingliquid, a solvent which is miscible with the developer and does notdissolve the resist film is preferred. Suitable solvents includealcohols of 3 to 10 carbon atoms, ether compounds of 8 to 12 carbonatoms, alkanes, alkenes, and alkynes of 6 to 12 carbon atoms, andaromatic solvents. Specifically, suitable alcohols of 3 to 10 carbonatoms include n-propyl alcohol, isopropyl alcohol, 1-butyl alcohol,2-butyl alcohol, isobutyl alcohol, t-butyl alcohol, 1-pentanol,2-pentanol, 3-pentanol, t-pentyl alcohol, neopentyl alcohol,2-methyl-1-butanol, 3-methyl-1-butanol, 3-methyl-3-pentanol,cyclopentanol, 1-hexanol, 2-hexanol, 3-hexanol, 2,3-dimethyl-2-butanol,3,3-dimethyl-1-butanol, 3,3-dimethyl-2-butanol, 2-ethyl-1-butanol,2-methyl-1-pentanol, 2-methyl-2-pentanol, 2-methyl-3-pentanol,3-methyl-1-pentanol, 3-methyl-2-pentanol, 3-methyl-3-pentanol,4-methyl-1-pentanol, 4-methyl-2-pentanol, 4-methyl-3-pentanol,cyclohexanol, and 1-octanol. Suitable ether compounds of 8 to 12 carbonatoms include di-n-butyl ether, diisobutyl ether, di-s-butyl ether,di-n-pentyl ether, diisopentyl ether, di-s-pentyl ether, di-t-pentylether, and di-n-hexyl ether. Suitable alkanes of 6 to 12 carbon atomsinclude hexane, heptane, octane, nonane, decane, undecane, dodecane,methylcyclopentane, dimethylcyclopentane, cyclohexane,methylcyclohexane, dimethylcyclohexane, cycloheptane, cyclooctane, andcyclononane. Suitable alkenes of 6 to 12 carbon atoms include hexene,heptene, octene, cyclohexene, methylcyclohexene, dimethylcyclohexene,cycloheptene, and cyclooctene. Suitable alkynes of 6 to 12 carbon atomsinclude hexyne, heptyne, and octyne. Suitable aromatic solvents includetoluene, xylene, ethylbenzene, isopropylbenzene, t-butylbenzene andmesitylene. The solvents may be used alone or in admixture.

Rinsing is effective for minimizing the risks of resist pattern collapseand defect formation. However, rinsing is not essential. If rinsing isomitted, the amount of solvent used may be reduced.

A hole or trench pattern after development may be shrunk by the thermalflow, RELACS® or DSA process. A hole pattern is shrunk by coating ashrink agent thereto, and baking such that the shrink agent may undergocrosslinking at the resist surface as a result of the acid catalystdiffusing from the resist layer during bake, and the shrink agent mayattach to the sidewall of the hole pattern. The bake is preferably at atemperature of 70 to 180° C., more preferably 80 to 170° C., for a timeof 10 to 300 seconds. The extra shrink agent is stripped and the holepattern is shrunk.

EXAMPLE

Examples of the invention are given below by way of illustration and notby way of limitation. The abbreviation “pbw” is parts by weight.

Iodonium salts of fluorinated aminobenzoic acid, fluorinatednitrobenzoic acid or fluorinated hydroxybenzoic acid, designatedQuenchers 1 to 16, used in resist compositions are identified below.Quenchers 1 to 16 were synthesized by ion exchange between a fluorinatedaminobenzoic acid, fluorinated nitrobenzoic acid or fluorinatedhydroxybenzoic acid providing the anion shown below and an iodoniumchloride providing the cation shown below.

Synthesis Example: Synthesis of Base Polymers (Polymers 1 to 5)

Base polymers were prepared by combining suitable monomers, effectingcopolymerization reaction thereof in tetrahydrofuran (THF) solvent,pouring the reaction solution into methanol for crystallization,repeatedly washing with hexane, isolation, and drying. The resultingpolymers, designated Polymers 1 to 5, were analyzed for composition by¹H-NMR spectroscopy, and for Mw and Mw/Mn by GPC versus polystyrenestandards using THF solvent.

EXAMPLES AND COMPARATIVE EXAMPLES

Resist compositions of positive or negative tone were prepared bydissolving the polymer and selected components in a solvent inaccordance with the recipe shown in Tables 1 and 2, and filteringthrough a filter having a pore size of 0.2 μm. The solvent contained 100ppm of surfactant FC-4430 (3M Sumitomo Co., Ltd.). The components inTables 1 and 2 are as identified below.

Organic Solvents:

-   -   PGMEA (propylene glycol monomethyl ether acetate)    -   GBL (γ-butyrolactone)    -   CyH (cyclohexanone)    -   PGME (propylene glycol monomethyl ether)        Acid generators: PAG1 and PAG2 of the following structural        formulae

Comparative Quenchers 1 to 8 of the following structural formulae

Water-Repellent Polymers 1 and 2

ArF Immersion Lithography Patterning Test

Examples 1-1 to 1-17 and Comparative Examples 1-1 to 1-9

On a substrate (silicon wafer), a spin-on carbon film ODL-102 (Shin-EtsuChemical Co., Ltd.) having a carbon content of 80 wt % was deposited toa thickness of 200 nm and a silicon-containing spin-on hard maskSHB-A940 having a silicon content of 43 wt % was deposited thereon to athickness of 35 nm. On this substrate for trilayer process, each of theresist compositions in Tables 1 and 2 was spin coated, then baked on ahotplate at 100° C. for 60 seconds to form a resist film of 80 nm thick.

Using an ArF excimer laser scanner NSR-S610C (Nikon Corp., NA 1.30, σ0.98/0.78, 35° cross-pole illumination, azimuthally polarizedillumination), the resist film was exposed through a 6% halftone phaseshift mask bearing a pattern having a line of 50 nm and a pitch of 100nm (on-wafer size) by immersion lithography. Water was used as theimmersion liquid. The resist film was baked (PEB) at the temperatureshown in Tables 1 and 2 for 60 seconds. Thereafter, the resist film wasdeveloped in n-butyl acetate for 30 seconds in Examples 1-1 to 1-16 andComparative Examples 1-1 to 1-8 or in 2.38 wt % tetramethylammoniumhydroxide (TMAH) aqueous solution in Example 1-17 and ComparativeExample 1-9, yielding a negative line-and-space (L/S) pattern having aspace of 50 nm and a pitch of 100 nm.

The pattern was observed under a CD-SEM (CG-4000, HitachiHigh-Technologies Corp.). The exposure dose capable of resolving a L/Spattern at 1:1 was determined as sensitivity, and edge roughness (LWR)was measured. The results are shown in Tables 1 and 2.

TABLE 1 Acid Water-repellent PEB Polymer generator Quencher polymerOrganic solvent temp. Sensitivity LWR (pbw) (pbw) (pbw) (pbw) (pbw) (°C.) (mJ/cm²) (nm) Example 1-1 Polymer 1 PAG 1 Quencher 1 Water-repellentPGMEA (2,200) 95 42 3.2 (100) (8.0) (4.50) polymer 1 GBL (300) (4.0) 1-2Polymer 1 PAG 1 Quencher 2 Water-repellent PGMEA (2,200) 95 41 3.0 (100)(8.0) (4.50) polymer 1 GBL (300) (4.0) 1-3 Polymer 1 PAG 1 Quencher 3Water-repellent PGMEA (2,200) 95 43 3.0 (100) (8.0) (4.50) polymer 1 GBL(300) (4.0) 1-4 Polymer 1 PAG 1 Quencher 4 Water-repellent PGMEA (2,200)95 38 2.2 (100) (8.0) (4.50) polymer 1 GBL (300) (4.0) 1-5 Polymer 1 PAG1 Quencher 5 Water-repellent PGMEA (2,200) 95 44 3.6 (100) (8.0) (4.50)polymer 1 GBL (300) (4.0) 1-6 Polymer 1 PAG 1 Quencher 6 Water-repellentPGMEA (2,200) 95 47 2.7 (100) (8.0) (4.50) polymer 1 GBL (300) (4.0) 1-7Polymer 1 PAG 1 Quencher 7 Water-repellent PGMEA (2,200) 95 48 3.0 (100)(8.0) (4.50) polymer 1 GBL (300) (4.0) 1-8 Polymer 1 PAG 1 Quencher 8Water-repellent PGMEA (2,200) 95 52 3.6 (100) (8.0) (4.50) polymer 1 GBL(300) (4.0) 1-9 Polymer 1 PAG 1 Quencher 9 Water-repellent PGMEA (2,200)95 46 2.2 (100) (8.0) (4.50) polymer 1 GBL (300) (4.0) 1-10 Polymer 1PAG 1 Quencher 10 Water-repellent PGMEA (2,200) 95 47 2.5 (100) (8.0)(4.50) polymer 1 GBL (300) (4.0) 1-11 Polymer 1 PAG 1 Quencher 11Water-repellent PGMEA (2,200) 95 45 2.8 (100) (8.0) (4.50) polymer 1 GBL(300) (4.0) 1-12 Polymer 1 PAG 1 Quencher 12 Water-repellent PGMEA(2,200) 95 43 2.1 (100) (8.0) (4.50) polymer 1 GBL (300) (4.0) 1-13Polymer 1 PAG 1 Quencher 13 Water-repellent PGMEA (2,200) 95 45 2.8(100) (8.0) (4.50) polymer 1 GBL (300) (4.0) 1-14 Polymer 1 PAG 1Quencher 14 Water-repellent PGMEA (2,200) 95 40 2.9 (100) (8.0) (4.50)polymer 1 GBL (300) (4.0) 1-15 Polymer 2 — Quencher 11 Water-repellentPGMEA (2,200) 100 36 2.6 (100) (4.50) polymer 1 GBL (300) (4.0) 1-16Polymer 3 PAG 1 Quencher 4 Water-repellent PGMEA (2,200) 90 38 2.1 (100)(6.0) (4.50) polymer 1 GBL (300) PAG 2 (4.0) (3.0) 1-17 Polymer 4 PAG 1Quencher 4 Water-repellent PGMEA (2,200) 100 42 3.6 (100) (8.0) (4.50)polymer 2 GBL (300) (4.0)

TABLE 2 Acid Water-repellent PEB Polymer generator Quencher polymerOrganic solvent temp. Sensitivity LWR (pbw) (pbw) (pbw) (pbw) (pbw) (°C.) (mJ/cm²) (nm) Comparative 1-1 Polymer 1 PAG 1 ComparativeWater-repellent PGMEA (2,200) 95 37 5.0 Example (100) (8.0) Quencher 1polymer 1 GBL (300) (2.13) (4.0) 1-2 Polymer 1 PAG 1 ComparativeWater-repellent PGMEA (2,200) 95 46 4.4 (100) (8.0) Quencher 2 polymer 1GBL (300) (2.13) (4.0) 1-3 Polymer 1 PAG 1 Comparative Water-repellentPGMEA (2,200) 95 38 4.3 (100) (8.0) Quencher 3 polymer 1 GBL (300)(4.50) (4.0) 1-4 Polymer 1 PAG 1 Comparative Water-repellent PGMEA(2,200) 95 42 4.5 (100) (8.0) Quencher 4 polymer 1 GBL (300) (4.50)(4.0) 1-5 Polymer 1 PAG 1 Comparative Water-repellent PGMEA (2,200) 9556 4.9 (100) (8.0) Quencher 5 polymer 1 GBL (300) (4.50) (4.0) 1-6Polymer 1 PAG 1 Comparative Water-repellent PGMEA (2,200) 95 39 4.6(100) (8.0) Quencher 6 polymer 1 GBL (300) (4.50) (4.0) 1-7 Polymer 1PAG 1 Comparative Water-repellent PGMEA (2,200) 95 31 4.8 (100) (8.0)Quencher 7 polymer 1 GBL (300) (4.50) (4.0) 1-8 Polymer 1 PAG 1Comparative Water-repellent PGMEA (2,200) 95 41 3.8 (100) (8.0) Quencher8 polymer 1 GBL (300) (4.50) (4.0) 1-9 Polymer 1 PAG 1 ComparativeWater-repellent PGMEA (2,200) 100 58 6.0 (100) (8.0) Quencher 7 polymer2 GBL (300) (4.50) (4.0)EB Lithography Test

Examples 2-1 to 2-5 and Comparative Examples 2-1 to 2-3

Each of the resist compositions in Table 3 was spin coated onto asilicon substrate, which had been vapor primed with hexamethyldisilazane(HMDS), and pre-baked on a hotplate at 110° C. for 60 seconds to form aresist film of 80 nm thick. Using a system HL-800D (Hitachi Ltd.) at anaccelerating voltage of 50 kV, the resist film was exposed imagewise toEB in a vacuum chamber. Immediately after the image writing, the resistfilm was baked (PEB) on a hotplate at 80° C. for 60 seconds anddeveloped in a 2.38 wt % TMAH aqueous solution for 30 seconds to form apattern.

The resist pattern was evaluated for sensitivity, resolution and LWR.The resolution is a minimum L/S size at the exposure dose that providesa resolution as designed of a 120-nm L/S pattern. The 120-nm L/S patternwas measured for LWR. The results are shown in Table 3.

TABLE 3 Polymer Acid generator Quencher Organic solvent SensitivityResolution LWR (pbw) (pbw) (pbw) (pbw) (μC/cm²) (nm) (nm) Example 2-1Polymer 5 — Quencher 4 PGMEA (400) 26 80 3.0 (100) (2.50) CyH (2,000)PGME (100) 2-2 Polymer 5 — Quencher 9 PGMEA (400) 33 80 2.8 (100) (2.50)CyH (2,000) PGME (100) 2-3 Polymer 5 — Quencher 12 PGMEA (400) 22 80 2.6(100) (2.50) CyH (2,000) PGME (100) 2-4 Polymer 5 — Quencher 15 PGMEA(400) 20 80 2.4 (100) (3.50) CyH (2,000) PGME (100) 2-5 Polymer 5 —Quencher 16 PGMEA (400) 18 80 2.5 (100) (3.50) CyH (2,000) PGME (100)Comparative 2-1 Polymer 5 — Comparative PGMEA (400) 38 90 5.0 Example(100) Quencher 1 CyH (2,000) (2.50) PGME (100) 2-2 Polymer 5 —Comparative PGMEA (400) 38 90 5.2 (100) Quencher 2 CyH (2,000) (2.50)PGME (100) 2-3 Polymer 5 — Comparative PGMEA (400) 38 90 5.5 (100)Quencher 3 CyH (2,000) (2.50) PGME (100)

It is demonstrated in Tables 1 to 3 that resist compositions comprisingan iodonium salt having formula (A) within the scope of the inventionoffer a satisfactory resolution and improved LWR.

Japanese Patent Application No. 2017-028673 is incorporated herein byreference.

Although some preferred embodiments have been described, manymodifications and variations may be made thereto in light of the aboveteachings. It is therefore to be understood that the invention may bepracticed otherwise than as specifically described without departingfrom the scope of the appended claims.

The invention claimed is:
 1. A resist composition comprising a basepolymer and a quencher containing an iodonium salt having the formula(A):

wherein R¹ is a nitro group, hydroxyl group or a group having theformula (A-1) below, R² is fluorine or trifluoromethyl, R³ is methyl orcyano, R⁴ is hydroxyl, halogen, trifluoromethyl, nitro, carboxyl, aC₂-C₁₀ acyl group, C₂-C₁₀ acyloxy group, C₂-C₁₀ alkoxycarbonyl group, astraight, branched or cyclic C₁-C₁₂ alkyl group which may contain oxo, astraight, branched or cyclic C₂-C₁₂ alkenyl group which may contain oxo,a straight, branched or cyclic C₁-C₁₂ alkoxy group, C₆-C₂₀ aryl group,or C₇-C₁₂ aralkyl or aryloxyalkyl group, R⁵ is an optionally substitutedphenyl group having the formula (A-2) below or an optionally substitutedethynyl group having the formula (A-3) below, m is an integer of 1 to 4,n is an integer of 0 to 3, and p is an integer of 0 to 5,

wherein R⁶ and R⁷ are each independently hydrogen or a straight,branched or cyclic C₁-C₆ alkyl group, R⁶ and R⁷ may bond together toform a ring with the nitrogen atom to which they are attached, whichring may contain an ether bond, R⁸ is hydroxyl, halogen,trifluoromethyl, nitro, carboxyl, a C₂-C₁₀ acyl group, C₂-C₁₀ acyloxygroup, C₂-C₁₀ alkoxycarbonyl group, a straight, branched or cyclicC₁-C₁₂ alkyl group which may contain oxo, a straight, branched or cyclicC₂-C₁₂ alkenyl group which may contain oxo, a straight, branched orcyclic C₁-C₁₂ alkoxy group, C₆-C₂₀ aryl group, or C₇-C₁₂ aralkyl oraryloxyalkyl group, R⁹ is hydrogen, hydroxyl, halogen, trifluoromethyl,nitro, carboxyl, a C₂-C₁₀ acyl group, C₂-C₁₀ acyloxy group, C₂-C₁₀alkoxycarbonyl group, a straight, branched or cyclic C₁-C₁₂ alkyl groupwhich may contain oxo, a straight, branched or cyclic C₂-C₁₂ alkenylgroup which may contain oxo, a straight, branched or cyclic C₁-C₁₂alkoxy group, C₆-C₂₀ aryl group, or C₇-C₁₂ aralkyl or aryloxyalkylgroup, and q is an integer of 0 to 5, wherein the base polymer comprisesrecurring units having the formula (a1) or recurring units having theformula (a2):

wherein R^(A) is each independently hydrogen or methyl, X¹ is a singlebond, phenylene group, naphthylene group, or C₁-C₁₂ linking groupcontaining an ester moiety and/or lactone ring, X² is a single bond orester group, R¹¹ and R¹² each are an acid labile group having theformula (AL-3),

wherein R¹⁷, R¹⁸ and R¹⁹ are each independently a monovalent hydrocarbongroup of 1 to 20 carbon atoms which may contain a heteroatom, a pair ofR¹⁷ and R¹⁸, R¹⁷ and R¹⁹, or R¹⁸ and R¹⁹ may bond together to form aring with the carbon atom to which they are attached, the ringcontaining 3 to 20 carbon atoms.
 2. The resist composition of claim 1,further comprising an acid generator capable of generating a sulfonicacid, imide acid or methide acid.
 3. The resist composition of claim 1,further comprising an organic solvent.
 4. The resist composition ofclaim 1, further comprising a dissolution inhibitor.
 5. The resistcomposition of claim 1 which is a chemically amplified positive resistcomposition.
 6. The resist composition of claim 1, further comprising asurfactant.
 7. A process for forming a pattern comprising the steps ofapplying the resist composition of claim 1 onto a substrate, baking toform a resist film, exposing the resist film to high-energy radiation,and developing the exposed film in a developer.
 8. The process of claim7 wherein the high-energy radiation is ArF excimer laser radiation ofwavelength 193 nm or KrF excimer laser radiation of wavelength 248 nm.9. The resist composition of claim 1 wherein R¹ is a group having theformula (A-1).
 10. The resist composition of claim 1 wherein R⁵ is anoptionally substituted ethynyl group having the formula (A-3).
 11. Aresist composition comprising a base polymer, a crosslinker and aquencher containing an iodonium salt having the formula (A):

wherein R¹ is a nitro group, hydroxyl group or a group having theformula (A-1) below, R² is fluorine or trifluoromethyl, R³ is methyl orcyano, R⁴ is hydroxyl, halogen, trifluoromethyl, nitro, carboxyl, aC₂-C₁₀ acyl group, C₂-C₁₀ acyloxy group, C₂-C₁₀ alkoxycarbonyl group, astraight, branched or cyclic C₁-C₁₂ alkyl group which may contain oxo, astraight, branched or cyclic C₂-C₁₂ alkenyl group which may contain oxo,a straight, branched or cyclic C₁-C₁₂ alkoxy group, C₆-C₂₀ aryl group,or C₇-C₁₂ aralkyl or aryloxyalkyl group, R⁵ is an optionally substitutedphenyl group having the formula (A-2) below or an optionally substitutedethynyl group having the formula (A-3) below, m is an integer of 1 to 4,n is an integer of 0 to 3, and p is an integer of 0 to 5,

wherein R⁶ and R⁷ are each independently hydrogen or a straight,branched or cyclic C₁-C₆ alkyl group, R⁶ and R⁷ may bond together toform a ring with the nitrogen atom to which they are attached, whichring may contain an ether bond, R⁸ is hydroxyl, halogen,trifluoromethyl, nitro, carboxyl, a C₂-C₁₀ acyl group, C₂-C₁₀ acyloxygroup, C₂-C₁₀ alkoxycarbonyl group, a straight, branched or cyclicC₁-C₁₂ alkyl group which may contain oxo, a straight, branched or cyclicC₂-C₁₂ alkenyl group which may contain oxo, a straight, branched orcyclic C₁-C₁₂ alkoxy group, C₆-C₂₀ aryl group, or C₇-C₁₂ aralkyl oraryloxyalkyl group, R⁹ is hydrogen, hydroxyl, halogen, trifluoromethyl,nitro, carboxyl, a C₂-C₁₀ acyl group, C₂-C₁₀ acyloxy group, C₂-C₁₀alkoxycarbonyl group, a straight, branched or cyclic C₁-C₁₂ alkyl groupwhich may contain oxo, a straight, branched or cyclic C₂-C₁₂ alkenylgroup which may contain oxo, a straight, branched or cyclic C₁-C₁₂alkoxy group, C₆-C₂₀ aryl group, or C₇-C₁₂ aralkyl or aryloxyalkylgroup, and q is an integer of 0 to 5, and wherein the base polymer isfree of an acid labile group.
 12. A resist composition comprising a basepolymer and a quencher containing an iodonium salt having the formula(A):

wherein R¹ is a nitro group, hydroxyl group or a group having theformula (A-1) below, R² is fluorine or trifluoromethyl, R³ is methyl orcyano, R⁴ is hydroxyl, halogen, trifluoromethyl, nitro, carboxyl, aC₂-C₁₀ acyl group, C₂-C₁₀ acyloxy group, C₂-C₁₀ alkoxycarbonyl group, astraight, branched or cyclic C₁-C₁₂ alkyl group which may contain oxo, astraight, branched or cyclic C₂-C₁₂ alkenyl group which may contain oxo,a straight, branched or cyclic C₁-C₁₂ alkoxy group, C₆-C₂₀ aryl group,or C₇-C₁₂ aralkyl or aryloxyalkyl group, R⁵ is an optionally substitutedphenyl group having the formula (A-2) below or an optionally substitutedethynyl group having the formula (A-3) below, m is an integer of 1 to 4,n is an integer of 0 to 3, and p is an integer of 0 to 5,

wherein R⁶ and R⁷ are each independently hydrogen or a straight,branched or cyclic C₁-C₆ alkyl group, R⁶ and R⁷ may bond together toform a ring with the nitrogen atom to which they are attached, whichring may contain an ether bond, R⁸ is hydroxyl, halogen,trifluoromethyl, nitro, carboxyl, a C₂-C₁₀ acyl group, C₂-C₁₀ acyloxygroup, C₂-C₁₀ alkoxycarbonyl group, a straight, branched or cyclicC₁-C₁₂ alkyl group which may contain oxo, a straight, branched or cyclicC₂-C₁₂ alkenyl group which may contain oxo, a straight, branched orcyclic C₁-C₁₂ alkoxy group, C₆-C₂₀ aryl group, or C₇-C₁₂ aralkyl oraryloxyalkyl group, R⁹ is hydrogen, hydroxyl, halogen, trifluoromethyl,nitro, carboxyl, a C₂-C₁₀ acyl group, C₂-C₁₀ acyloxy group, C₂-C₁₀alkoxycarbonyl group, a straight, branched or cyclic C₁-C₁₂ alkyl groupwhich may contain oxo, a straight, branched or cyclic C₂-C₁₂ alkenylgroup which may contain oxo, a straight, branched or cyclic C₁-C₁₂alkoxy group, C₆-C₂₀ aryl group, or C₇-C₁₂ aralkyl or aryloxyalkylgroup, and q is an integer of 0 to 5, wherein the base polymer is freeof an acid labile group, and wherein the resist composition is achemically amplified negative resist composition.
 13. A resistcomposition comprising a base polymer and a quencher containing aniodonium salt having the formula (A):

wherein R¹ is a nitro group, hydroxyl group or a group having theformula (A-1) below, R² is fluorine or trifluoromethyl, R³ is methyl orcyano, R⁴ is hydroxyl, halogen, trifluoromethyl, nitro, carboxyl, aC₂-C₁₀ acyl group, C₂-C₁₀ acyloxy group, C₂-C₁₀ alkoxycarbonyl group, astraight, branched or cyclic C₁-C₁₂ alkyl group which may contain oxo, astraight, branched or cyclic C₂-C₁₂ alkenyl group which may contain oxo,a straight, branched or cyclic C₁-C₁₂ alkoxy group, C₆-C₂₀ aryl group,or C₇-C₁₂ aralkyl or aryloxyalkyl group, R⁵ is an optionally substitutedphenyl group having the formula (A-2) below or an optionally substitutedethynyl group having the formula (A-3) below, m is an integer of 1 to 4,n is an integer of 0 to 3, and p is an integer of 0 to 5,

wherein R⁶ and R⁷ are each independently hydrogen or a straight,branched or cyclic C₁-C₆ alkyl group, R⁶ and R⁷ may bond together toform a ring with the nitrogen atom to which they are attached, whichring may contain an ether bond, R⁸ is hydroxyl, halogen,trifluoromethyl, nitro, carboxyl, a C₂-C₁₀ acyl group, C₂-C₁₀ acyloxygroup, C₂-C₁₀ alkoxycarbonyl group, a straight, branched or cyclicC₁-C₁₂ alkyl group which may contain oxo, a straight, branched or cyclicC₂-C₁₂ alkenyl group which may contain oxo, a straight, branched orcyclic C₁-C₁₂ alkoxy group, C₆-C₂₀ aryl group, or C₇-C₁₂ aralkyl oraryloxyalkyl group, R⁹ is hydrogen, hydroxyl, halogen, trifluoromethyl,nitro, carboxyl, a C₂-C₁₀ acyl group, C₂-C₁₀ acyloxy group, C₂-C₁₀alkoxycarbonyl group, a straight, branched or cyclic C₁-C₁₂ alkyl groupwhich may contain oxo, a straight, branched or cyclic C₂-C₁₂ alkenylgroup which may contain oxo, a straight, branched or cyclic C₁-C₁₂alkoxy group, C₆-C₂₀ aryl group, or C₇-C₁₂ aralkyl or aryloxyalkylgroup, and q is an integer of 0 to 5, wherein the base polymer furthercomprises recurring units of at least one type selected from theformulae (f1) to (f3):

wherein R^(A) is each independently hydrogen or methyl, Z¹ is a singlebond, phenylene group, —O—Z¹¹— or —C(═O)—Z¹²—Z¹¹—, Z¹¹ is (1) astraight, branched or cyclic C₁-C₆ alkylene which may contain acarbonyl, ester, ether or hydroxy moiety, (2) a straight, branched orcyclic C₂-C₆ alkenylene group which may contain a carbonyl, ester, etheror hydroxy moiety, or (3) a phenylene group, Z¹² is —O— or —NH—, R²¹,R²², R²³, R²⁴, R²⁵, R²⁶, R²⁷ and R²⁸ are each independently a straight,branched or cyclic C₁-C₁₂ alkyl group which may contain a carbonyl,ester or ether moiety, or C₆-C₁₂ aryl group or C₇-C₂₀ aralkyl group, inR²¹, R²², R²³, R²⁴, R²⁵, R²⁶, R²⁷ and R²⁸ at least one hydrogen may besubstituted by a C₁-C₁₀ straight, branched or cyclic alkyl moiety,halogen, trifluoromethyl, cyano, nitro, hydroxyl, mercapto, C₁-C₁₀straight, branched or cyclic alkoxy moiety, C₂-C₁₀ straight, branched orcyclic alkoxycarbonyl moiety, or C₂-C₁₀ straight, branched or cyclicacyloxy moiety, R²³ and R²⁴, or R²⁶ and R²⁷ may bond together directlyor via a methylene moiety or ether bond to form a ring with the sulfuratom to which they are attached, Z² is a single bond, —Z²¹—C(═O)—O—,—Z²¹—O— or —Z²¹—O—C(═O)—, Z²¹ is a straight, branched or cyclic C₁-C₁₂alkylene group which may contain a carbonyl, ester or ether moiety, Z³is a single bond, methylene group, ethylene group, phenylene group,fluorinated phenylene group, —O—Z³¹—, or —C(═O)—Z³²-Z³¹—, Z³¹ is (1) astraight, branched or cyclic C₁-C₆ alkylene group which may contain acarbonyl, ester, ether, fluorine or hydroxyl moiety, (2) a straight,branched or cyclic C₂-C₆ alkenylene group which may contain a carbonyl,ester, ether, fluorine or hydroxyl moiety, (3) a phenylene group, (4) afluorinated phenylene group or (5) a trifluoromethyl-substitutedphenylene group, Z³² is —O— or —NH—, A¹ is hydrogen or trifluoromethyl,and M⁻ is a non-nucleophilic counter ion.
 14. A process for forming apattern comprising the steps of applying a resist composition onto asubstrate, baking to form a resist film, exposing the resist film tohigh-energy radiation, and developing the exposed film in a developer,wherein the high-energy radiation is electron beam or extremeultraviolet radiation of wavelength 3 to 15 nm, and wherein the resistcomposition comprises a base polymer and a quencher containing aniodonium salt having the formula (A):

wherein R¹ is a nitro group, hydroxyl group or a group having theformula (A-1) below, R² is fluorine or trifluoromethyl, R³ is methyl orcyano, R⁴ is hydroxyl, halogen, trifluoromethyl, nitro, carboxyl, aC₂-C₁₀ acyl group, C₂-C₁₀ acyloxy group, C₂-C₁₀ alkoxycarbonyl group, astraight, branched or cyclic C₁-C₁₂ alkyl group which may contain oxo, astraight, branched or cyclic C₂-C₁₂ alkenyl group which may contain oxo,a straight, branched or cyclic C₁-C₁₂ alkoxy group, C₆-C₂₀ aryl group,or C₇-C₁₂ aralkyl or aryloxyalkyl group, R⁵ is an optionally substitutedphenyl group having the formula (A-2) below or an optionally substitutedethynyl group having the formula (A-3) below, m is an integer of 1 to 4,n is an integer of 0 to 3, and p is an integer of 0 to 5,

wherein R⁶ and R⁷ are each independently hydrogen or a straight,branched or cyclic C₁-C₆ alkyl group, R⁶ and R⁷ may bond together toform a ring with the nitrogen atom to which they are attached, whichring may contain an ether bond, R⁸ is hydroxyl, halogen,trifluoromethyl, nitro, carboxyl, a C₂-C₁₀ acyl group, C₂-C₁₀ acyloxygroup, C₂-C₁₀ alkoxycarbonyl group, a straight, branched or cyclicC₁-C₁₂ alkyl group which may contain oxo, a straight, branched or cyclicC₂-C₁₂ alkenyl group which may contain oxo, a straight, branched orcyclic C₁-C₁₂ alkoxy group, C₆-C₂₀ aryl group, or C₇-C₁₂ aralkyl oraryloxyalkyl group, R⁹ is hydrogen, hydroxyl, halogen, trifluoromethyl,nitro, carboxyl, a C₂-C₁₀ acyl group, C₂-C₁₀ acyloxy group, C₂-C₁₀alkoxycarbonyl group, a straight, branched or cyclic C₁-C₁₂ alkyl groupwhich may contain oxo, a straight, branched or cyclic C₂-C₁₂ alkenylgroup which may contain oxo, a straight, branched or cyclic C₁-C₁₂alkoxy group, C₆-C₂₀ aryl group, or C₇-C₁₂ aralkyl or aryloxyalkylgroup, and q is an integer of 0 to 5.